Vascular endothelial cells respond to ischemic stress in tissues by undergoing an angiogenic repair process. We have previously shown that activation of Akt signaling is an important mediator of the angiogenic response in endothelial cells. More recently, we have shown that hypoxia and hypoxic-reoxygenation are powerful stimuli of AMP-activated kinase (AMPK) signaling within endothelial cells, and that AMPK signaling significantly contributes to biological responses in endothelial cells under conditions of ischemic stress including eNOS activation, cellular survival and migration. Based upon these data, it has been proposed that AMPK signaling promotes endothelial cell function and angiogenic responses in ischemic tissues. Recent studies have shown that LKB1 functions as a key regulator of both AMPK and Akt signaling in a number of tissues including liver, skeletal muscle, myocardium and various cancers. However, very little is known about the role of LKB1 in regulating endothelial cell function and angiogenic responses. Thus, we will investigate the role of LKB1 in endothelial cells biology in vitro utilizing adenoviral expression vectors and siRNA procedures to understand how this signaling step regulates AMPK and Akt pathways under conditions of normoxia and hypoxia. A series of related experiments will analyze the role of LKB1 in endothelial cell function in vitro including NO production, survival, migration and proliferation. To understand the role of vascular cell LKB1 signaling in vivo, endothelial LKB1-knockout mice will be created using a cre/lox approach, and their baseline phenotype will be assessed. Finally, endothelial LKB1-deficient mice will be subjected to ischemic stresses and vascular responses will be evaluated. PUBLIC HEALTH RELEVANCE Vascular endothelial cells respond to ischemic stress in tissues by undergoing an angiogenic repair process. A series of experiments will analyze the role of LKB1 in endothelial cell function. LKB1-knockout mice will be created and their baseline phenotype will be assessed. Endothelial LKB1-deficient mice will be subjected to ischemic stresses and vascular responses will be evaluated.